1. Field of the Invention
The present invention relates generally to position sensing and indicating devices and, more particularly, is concerned with a self-setting switch-actuating assembly and a method of self-setting a pair of actuating cams of the actuating assembly relative to a pair of switches.
2. Description of the Prior Art
It is conventional practice to use actuation of micro or limit switches to control positioning of a rotatable valve at a selected one of its opened and closed conditions. Typically, a pair of angularly displaced cams are integrally formed or rigidly attached, on a shaft coupled for rotation with a rotatable stem of the valve. As the shaft rotates in either a clockwise or counterclockwise direction with the valve stem, the actuating cams will move either clockwise or counterclockwise along a path which brings one or the other of the cams into contact with one or the other of the limit switches, causing the stem of the valve to stop and thereby place the valve at either its opened or closed condition. Representative of such cam arrangements in the prior patent art for actuating limit switches to control valve position are the ones disclosed in U.S. Pat. Nos. to Grassel et al (3,429,335), Weekley (3,484,075), Fujiwara (3,680,831), Broe (3,870,274), Wilhelm (4,407,326), van Lingen (4,556,194), Fukamachi (4,621,789) and Bajka (4,647,007).
These same arrangements are also used to actuate limit switches for sensing when rotational components such as a valve stem has reached either its opened or closed condition so that indicator lights can be turned on and off or status signals transmitted to a computer. However, most of these arrangements require performance of complicated procedures for initial setup of the angular orientation of the cams and their mounting shaft relative to the rotational position of the valve stem to ensure proper actuation of the limit switches. Also, periodically, the setup must be examined and, if needed, adjustments made. The initial setup of the arrangement and its periodic examination requires careful and accurate initial assembling and subsequent reassembling of parts which is time-consuming and subject to human error.
Consequently, a need exists for a more reliable and substantially error-free way of ensuring accurate actuation of the limit switches for controlling valve stem position.